WASHINGTON (Reuters) - Japan's Diamond Electric Manufacturing Co Ltd <6895.T> has agreed to plead guilty and pay a $19 million (12.57 million pounds) criminal fine for a conspiracy to fix prices of ignition coils sold to Ford Motor Co (>> Ford Motor Company) and other companies, the U.S. Justice Department said on Tuesday.

Diamond is the 10th auto-parts maker to agree to plead guilty in the Justice Department's long-running investigation into price-fixing in the industry.

Separately, an executive with Autoliv Inc (>> Autoliv Inc.), Takayoshi Matsunaga, agreed to plead guilty in connection with a conspiracy to fix the prices of seat belts sold to Toyota Motor Corp (>> TOYOTA MOTOR CORPORATION), the Justice Department said.

Matsunaga, who pleaded guilty to a single felony, is the 15th executive to acknowledge breaking the law as part of the probe.

Diamond Electric, which agreed to assist the Justice Department, agreed to plead guilty to a single felony charges of fixing the prices of ignition coils sold to Ford, Toyota Motor Corp and Fuji Heavy Industries Ltd, the Justice Department said.

The department said the price fixing conspiracy ran from at least July 2003 to at least February 2010.

The nine auto parts makers that have already pleaded guilty are Tokai Rika (>> TOKAI RIKA CO., LTD.), Autoliv (>> Autoliv Inc.), TRW Deutschland Holding GmbH, Nippon Seiki Co Ltd, Fujikura Ltd (>> Fujikura Ltd), Furukawa Electric Co Ltd (>> Furukawa Electric Co Ltd), Denso Corp (>> Denso Corporation), Yazaki Corp and G.S. Electech.

(Reporting by David Ingram and Diane Bartz; Editing by Gerald E. McCormick and David Gregorio)